A review of Canadian and Alaskan species of the genera Clusiota Casey and Atheta Thomson, subgenus Microdota Mulsant & Rey (Coleoptera, Staphylinidae, Aleocharinae)

Abstract This paper treats 13 species of the subgenus Microdota Mulsant & Rey of Atheta Thomson and 3 species of the genus Clusiota Casey in Canada and Alaska. We report here 4 species new to science, and 3 new provincial records. The following species are new to science: Atheta (Microdota) curtipenis Klimaszewski & Webster, sp. n., Atheta (Microdota) formicaensis Klimaszewski & Webster, sp. n., Atheta (Microdota) macesi Klimaszewski & Webster, sp. n., and Clusiota grandipenis Klimaszewski & Webster, sp. n. The new provincial records are: Atheta (Microdota) pseudosubtilis Klimaszewski & Langor, new to AB, and Atheta (Microdota) subtilis (Scriba), an adventive Palaearctic species new to North America, first reported in LB and NB. The two Clusiota Casey species are reviewed, and their distribution is revised. A female Clusiota impressicollis was discovered in Ontario and is illustrated here for the first time. A key to all Canadian species of the subgenus Microdota and genus Clusiota are provided. Atheta (Microdota) holmbergi Bernhauer and Atheta (Microdota) alesi Klimaszewski & Brunke are transferred here to the subgenus Dimetrota Mulsant & Rey.


Introduction
Aleocharines are species rich in the boreal forest of Canada but knowledge of them, despite recent progress (Klimaszewski et al. 2015), is still fragmentary and there are many species likely to be discovered as new to science or as new records of adventive or formerly known species from the USA (Klimaszewski et al. 2015).
This paper deals with Canadian species of the subgenus Microdota Mulsant and Rey of the genus Atheta Thomson and Rey, and the genus Clusiota Casey occurring in Canada and Alaska. The subgenus Microdota contains about 215 species in the Palaearctic region (Lee and Ahn 2015). In the Nearctic region the true number of species is unknown but Ashe (2000) reported 27 species. Microdota species may be confused with those of Clusiota due to their small size, and other superficial similarities. That is why both groups are treated here. Microdota species may also be confused with members of the subgenus Datomicra Mulsant and Rey from which they may be separated by having a fully exposed pronotal hypomeron in lateral view, whereas in Datomicra it is only partially exposed (Seevers 1978, Ashe 2000. In Canada we recognize 13 Microdota species including 3 species described here as new to science, and 3 species of Clusiota, including one species new to science. These Clusiota species constitute all known Nearctic species of the genus. We provide diagnoses of new or newly recorded species, illustrations of habitus and genital structures of all Microdota species, and keys to their identification. We hope that this publication will lead to the proper identification of species in this difficult group and will make them available for ecological, environmental, and other studies.

Materials and methods
About 100 adults of the genera Microdota and Clusiota from Canada and Alaska were studied, and most specimens were dissected to examine the genitalic structures that were dehydrated in absolute alcohol, mounted in Canada balsam on celluloid microslides, and pinned with the specimens from which they originated. Images of the entire body and the genital structures were taken using an image processing system (Nikon SMZ 1500 stereoscopic microscope; Nikon Digit-like Camera DXM 1200F, and Adobe Photoshop software).
Some species of Microdota, due to small body size and some superficial external similarity, may be confused in collections with members of the subgenus Datomicra Mulsant and Rey, from which they may be distinguished by having a fully exposed pronotal hypomeron in lateral view; the pronotal hypomeron is only partially visible in Datomicra. Many species of Datomicra also have a more densely and coarsely punctate forebody than that of Microdota.
Microdota may be distinguished from Dimetrota by the following combination of characters: body usually parallel-sided, small, on average 2 mm long (Microdota -1.5-2.8 mm; Dimetrota -1.8-3.8 mm, with elytra usually distinctly broader than pronotum); glossae Y-shaped (deeply split in Dimetrota); pronotum with sparse to moderately dense and slightly asperate punctation (dense and strongly asperate in Dimetrota); lateral margins of pronotum and elytra, and middle and hind tibiae with moderately pronounced macrosetae (strong bristles in Dimetrota); hypomera fully visible in lateral view (partially to less often fully visible in Dimetrota); and male tergite VIII truncate apically, rarely crenulated, and usually without large lateral teeth (with two large lateral teeth and often distinctive form of margin between them or with pattern of smaller teeth in Dimetrota). Details on diagnostics of Microdota are provided by Brundin (1948), and Lee and Ahn (2015). Species of Nearctic Dimetrota badly need revision.
Clusiota may be distinguished from Microdota by the following combination of characters: basal antennal article swollen (some species); antennal articles V-X strongly transverse; glossae deeply split medially; pronotum narrower than elytra; elytra flattened, truncate posteriorly and without distinct lateral emargination; abdomen often swollen; spermatheca more or less sinuate with narrowly pear-shaped capsule and small and short apical invagination; and by the median lobe of the aedeagus with large bulbus, strongly ventrally produced tubus bearing elongate subapical part, and with crista apicalis located on elevated part of bulbus.
Natural history. The LB specimens were collected in flight intercept traps set in spruce-poplar forest. The NB specimens were found in gilled mushrooms at various stages of decay in spruce/fir forest, in Pleurotus sp. on dead standing P. tremuloides, in mixed forest on flowers of S. alba, and in a mixed forest with red spruce and yellow birch. Adults were captured from July to September.
Distribution. Atheta (M.) subtilis is a Palaearctic species (for details, see Brundin 1948, Palm 1970, Benick and Lohse 1974, Smetana 2004, and it is reported here as adventive for the first time from Canada (LB, NB) and North America.
Comments. Adults of A. subtilis from LB were captured in association with A. pseudosubtilis Klimaszewski and Langor. Some females of the former species, because of similarly shaped spermatheca and poorly preserved body, were misidentified as the latter species. We have compared European specimens of A. subtilis with those from Canada (LB, NB) and found no significant differences in external morphology and shape and structures of genitalia.
Comments. The taxonomic position of A. pseudosubtilis is somewhat unclear. The shape of the spermatheca is very similar to those of A. subtilis and C. antennalis. Externally it is similar to C. antennalis but does not have a swollen basal antennal article. The median lobe of the aedeagus has internal sac structures very similar to those of A. subtilis. Externally, A. pseudosubtilis is readily distinguished from A. subtilis by the much shorter elytra (Figs 1, 9). DNA studies of all these species would be very useful in revealing their true relationships.
Natural history. Adults were found in an eastern white cedar swamp under moose dung in May.
Distribution. Known only from NB, Canada.
Comments. This species is distinguished by the moderately transverse pronotum, and the shape of the median lobe of the aedeagus and spermatheca. Distribution. In Canada, recorded from AB, BC, LB, NB, NF, NS, ON, SK, YT, and in USA from AK (Klimaszewski et al. , 2015.

Atheta (Microdota) pratensis (Mäklin, 1852)
Homalota pratensis Mäklin, 1852: 308. As Atheta (Microdota): Moore andLegner 1975, Klimaszewski et al. 2011;Bousquet et al. 2013. Diagnosis. This species may be readily separated from other Nearctic congeners by the following combination of characters: pronotum rounded and margined, as wide as head and at least 1.5 times narrower than elytra; elytra elongate about twice as long as pronotum with wavy pattern of pubescence posteriorly; male tergite VIII truncate apically; sternite VIII rounded apically; median lobe of aedeagus with large oval bulbus and small triangular tubus in dorsal view, apical part of tubus narrow and  produced ventrally in lateral view; female tergite VIII truncate apically, and sternite VIII rounded apically and with antecostal suture sinuate and pointed medially; spermatheca S-shaped with club-shaped capsule bearing deep invagination and sinuate stem looped posteriorly, similar to that of A. platonoffi.
Comments. This species is somewhat similar to A. subtilis but may readily be distinguished externally by having elytra about 1.5 times wider and almost twice longer than pronotum. We examined the type series but the specimens were in poor shape and therefore were not illustrated.
Comments. All known Canadian specimens of Atheta festinans are females. Gusarov (2003b) remarked that all specimens seen of this species were females and suggested that this species may be parthenogenetic. Etymology. The specific name formicaensis is a feminine adjective derived from the generic name Formica, an ant genus found in association with the type series.
Natural history. Adults were found in association with nests of black ants in the genus Formica in April and May.

Distribution. Known only from NB, Canada.
Comments. This species is probably closely associated with nests of the ant genus Formica. It is distinguished from all other Nearctic species of Microdota by the shape of the median lobe of the aedeagus and spermatheca. The shape of the spermatheca is similar to that of Palaearctic A. (M.) glabricula Thomson (Palm 1970). Distribution. This species was recorded in Canada from NB, NF, NS, ON, QC, and in the USA from MN, NY, PA, VT (Gusarov 2003b.

Sculptisoma species group (new)
Species of this group are characterized by elytra at suture at least as long as pronotum (Fig. 80), male unknown; spermatheca pipe-shaped with hemispherical capsule narrowed basally and without apparent apical invagination, and with long stem that is looped posteriorly and twisted apically (Fig. 83). One species belongs to this group. Distribution. This native Nearctic species was recorded only from the type locality in southeastern NF in Canada .

Macesi species group (new)
Species of this group are characterized by the strongly glossy body, elytra at suture slightly longer than pronotum (Fig. 84), male tergite VIII truncate apically and with two small lateral teeth (Fig. 85), median lobe of aedeagus with small bulbus and elongate tubus, in lateral view tubus straight, apex narrowly triangular and slightly pointed (Fig. 87), internal sac structures pronounced (Fig. 87); female unknown. One species belongs to this group.   Bay, 45.1161N, 66.4560 W, 8.V.2006. // Eastern white cedar swamp, in sphagnum and litter near brook (LFC).
Etymology. The specific name macesi is an adjective derived from Maces Bay in NB, where the holotype specimen was found.
Diagnosis. Body length 2.7 mm, subparallel, flattened, brownish-black, tibiae and tarsi brown (Fig. 84); integument glossy and more so on abdomen, sparsely punctate and pubescent, except for pronotum and elytra; microsculpture of forebody dense and strong, meshed with hexagonal sculpticells; head about as wide as pronotum, slightly angular posteriorly, eyes large and as long as postocular area dorsally; antennae with articles V−X moderately to strongly transverse; pronotum broadest in apical third and narrowest at base, rounded laterally and basally, transverse, narrower than elytra; elytra wider and slightly longer than pronotum; abdomen subparallel. MALE. Tergite VIII truncate apically and with two large lateral teeth (Fig. 85); sternite VIII rounded apically (Fig. 86); median lobe of aedeagus with small bulbus and long tubus, in lateral view tubus straight and apex slightly produced ventrally, apex narrowly triangular and slightly pointed (Fig. 87), internal sac structures well defined (Fig. 87). FEMALE. Unknown.
Natural history. A single male was found in eastern white cedar in sphagnum and litter near a brook, in May.
Distribution. Known only from NB, Canada.

Genus Clusiota Casey
Comments. Species of this genus may be confused with Microdota species, from which they may be readily distinguished by the swollen first basal antennal articles (except for C. grandipenis), and shape of genitalia, with median lobe bearing large crista apicalis of bulbus. Casey (1910) believed this genus was related to the subgenus Datomicra of Atheta. Distribution. BC, NB, NF, ON (Casey 1910.

Key to Nearctic species of Clusiota
Natural history. The specimens from ON were collected in August. The NF specimens were captured in a light flight intercept trap in fir-deciduous forest in July/August . These records indicate that adults occur late in the season.
Comments. This species was originally reported by Bernhauer (1907) from Baring, WA and Pasadena, CA. The previously unknown female is illustrated here for the first time from a specimen from Mattagami, ON.  . It is here newly reported in Canada from BC, and from new localities in AK. Clusiota antennalis is a western Nearctic species known only from western BC and AK. Natural history. In AK, the holotype was captured in alder litter, and the recent AK specimens were collected primarily in pitfall traps from old-growth Pacific rain forests at low elevations although two specimens were collected in an alpine habitat above 650 m elevation. In BC, specimens from Vancouver Island were captured continuously from June to November in pitfall and pan traps.

Clusiota antennalis Klimaszewski & Godin
Comments. Females of this species have a spermatheca extremely similar to those of Atheta (M.) subtilis and A. (M.) pseudosubtilis. Clusiota antennalis is easily separated from the two species by the swollen basal antennal article (Fig. 96), and from A. subtilis by much shorter elytra (Fig. 96). It differs from all Nearctic Clusiota and Microdota species by the shape of the genitalia. Etymology. The specific name grandipenis, meaning large penis, refers to the large tubus of the median lobe of the aedeagus of this species.
Natural history. One adult was found in the nest contents of a Great Horned Owl, -Bubo virginensis in a black spruce forest in May and another from a decaying gilled mushroom in a jack pine forest during August.
Distribution. Known only from NB, Canada.